Your question was answered by lexico so you don't really need this particular Briton's input. Nevertheless you should specify what a 'Shuttle' PC is. I know, since they're all made in Taiwan, and are commonplace here in Japan - but only really in computer hobby shops and electric towns in the large cities.
The power switch on the reverse will toggle for use here. However, what are you planning to use for a display? Are you bringing that with you too? Even a TFT is a bulky item taking up a fair bit of luggage space. You can pick up a used 17" CRT monitor here for about 20 quid. Used 15" TFT monitors for around 50 quid (in fact I have one for sale - PM me for details). If determined to bring your existing TFT monitor it'll probably work fine - just check the voltage input on the AC adaptor.
BTW if you're going to be working in a school, on the JET program for example, then you should really go for a notebook computer. Surf at school for free. (I also sell those - new and used).